Sorry for the late reply. The event was BSides Ottawa; an attendee forwarded the challenges to me and made writeups of the crypto challenges here: https://rctcw

Sorry for the late reply. The event was BSides Ottawa; an attendee forwarded the challenges to me and made writeups of the crypto challenges here: https://rctcwyvrn.github.io/posts/2019-12-02-bsides_crypto.html https://rctcwyvrn.github.io/posts/2019-12-02-bsides_crypto.h.... The challenge was quite straightforward; they created a secure random key, displayed an encrypted flag, then let you en/decipher anything you wanted except the encrypted flag (NDS is symmetric so encryption = decryption). Some of the latest crypto-heavy CTFs have also featured pretty sophisticated "fundamental" attacks on ciphers. I've seen attacks on custom LCG-based stream ciphers (Google CTF), fancy math attacks on RSA variants (hxp 36C3 CTF just last week), and even the odd differential attack. Good crypto CTF challenges are really interesting and are great opportunities to learn and build classic attacks :)